Valarin was the tongue of the Ainur, and the oldest of languages. While the Valar were angelic beings with the ability to communicate through thought, a spoken language was unnecessary. Valarin was developed as part of their assumption of physical forms.
However, the Elves found Valarin alien, sometimes unpleasant, with very few of them ever deigning to learn the language. Some Valarin words were adopted by the Elves as part of the growing Quenya lexicon, particularly by the Vanyar. The Valar learnt Quenya instead to converse with the Elves or with each other if Elves were present.
It was not just the Elves who borrowed from Valarin. When Melkor and Sauron devised the Black Speech, at least one word, nazg (ring) was borrowed from the Valarin equivalent (naškad). As Ainur, both Melkor and Sauron would have spoken Valarin.
Valarin bears no relation to any of the other Languages of Middle-earth as it arose beyond Arda. Little is known of it, save a few words (mainly proper names) although it seems that Valarin used lengthy constructions. The Valarin word for Telperion is, for example, Ibrîniðilpathânezel, which is eight syllables long.
The only language before Valarin was the Music of the Ainur, the purest form of language as it was thought itself with a self-sufficient structure. Eru Ilúvatar only showed the Ainur their music in a different form by adding the final note to their song: Eä, "Be".
In the older versions of The Silmarillion and in the Lhammas, it is shown that Valarin was further subdivided into three categories: Oromëan, Aulëan and Melkian, with all Elven languages arising from the first category. J.R.R. Tolkien later rejected this view.